Accurate heat capacity data at phase transitions from relaxation calorimetry

Extracting accurate heat capacities by conventional relaxation calorimetry at first-order or very sharp second-order phase transitions is extremely difficult. The so-called “scanning method” provides a key to overcome this challenge. Here, we introduce new corrections in the data analysis of this method. Critical examinations of the improvements are made experimentally by investigating the well-studied first-order ferroelectric phase transitions of KH2PO4 and BaTiO3 using a commercial relaxation calorimeter Physical Property Measurement System (PPMS) supplied by Quantum Design. The results for KH2PO4 are shown to be excellent; a very sharp peak in heat capacity is obtained and the absolute values are shown to agree well with the previous results obtained by adiabatic calorimetry on much larger samples. The critical behavior of the heat capacity in the vicinity of the transition temperature, as well as the thermodynamic quantities such as the transition enthalpy and entropy, also agrees very well with the previous results. For BaTiO3, clear hysteretic behavior of the transition is observed for heating and cooling curves.